Actually the "better to remain silent" quote is originally from a children's book "Mrs. Goose: Her Book" (1906) by Maurice Switzer: http://quoteinvestigator.com/2010/05/17/remain-silent/. It's based on Proverbs 17:28.

Most of Hitler's ideas came Charles Darwin and local German and Austrian politicians, writers, and even musicians such as Richard Wagner.

https://www.ushmm.org/wlc/en/article.php?ModuleId=10007430
https://www.csustan.edu/history/roots-hitlers-evil
http://www.historytoday.com/jayne-rosefield/wagners-influence-hitler-and-hitlers-wagner
http://www.history.ucsb.edu/faculty/marcuse/classes/133p/133p04papers/MKalishNietzNazi046.htm

But for specific policies, it was recent American history that influenced him, such as American Indian reservations/concentration camps, Henry Ford and his anti-Semitic newspaper, etc.

http://www.cracked.com/article_23252_5-a...wing-it_p2.html